What is Time-Domain Science?

Whereas many astrophysical processes take eons to unfold — very long compared to the typical lifetime of humans — and the night sky, corrected for the diurnal and annual motion of the Earth, might be perceived as largely unchanging, there are, in fact, many phenomena that cause the brightness or position of objects to change with time on a variety of time-scales. Examples include variable stars and transients such as novae, supernovae, and gamma ray bursts; flickering of active galactic nuclei, and tidal disruption events when a supermassive black hole in the center of a galaxy shreds a star that ventures too close; blobs of matter ejected along jets from young stars and from supermassive black holes; small objects that change position within our own solar system such as asteroids and comets; and nearby stars that move with respect to the background of more distant Galactic stars; and even the minute motions of nearby galactic neighbours.

The study of all such objects and more, where important scientific information can be gleaned from their change over time, can be termed time-domain science. Time-domain science can be the long-term follow-up of an individual object discovered (or predicted) to flare, vary, or move, or involve long-term monitoring of a wide field on the sky that contains many thousands of objects, only a small percentage of which will show any change between any pair of subsequent observations. In the latter case, by combining such monitoring observations accumulated over time, one can also build a very deep map of the (more) static denizens of our universe.

The James Webb Space Telescope (JWST) North Ecliptic Pole (NEP) Time-Domain Field (TDF) by design is located within JWST's northern Continuous Viewing Zone, to facilitate long-term monitoring on any time-scale from hours to perhaps up to 20 years, while leveraging JWST's extreme sensitivity to open up a new portion of parameter space that uniquely complements existing and planned observing facilities on the ground and in space.